In a paper on electrolyte effects in reactions between a non-electrolyte and the hydrogen ion2 two typical examples were given, representative of electrolyte effects in (1) reactions showing specific catalysis by the hydrogen ion, and (2) reactions showing acid catalysis in the general sense. This classification has been clarified by experiments in solutions of heavy waterla and by Pedersen's analysis of prototropic reactions.'From an examination of the electrolyte effects it appeared that the inversion of sucrose and the hydrolysis of the acetals should be considered purely as catalysis by the hydrogen ion. Evidence of catalytic effects of acid molecules has been advanced by Hammett and Paull6 and by Gross, Steiner and Suess.' Experiments on the inversion of sucrose in acetateacetic acid buffer solutions have shown, however, there is no detectable catalytic effect of the molecules of such a weak acid as acetic?If we are dealing with a case of specific hydrogen-ion catalysis, we can for aqueous solutions postulate the equilibriumwhere kz << kand the equilibrium concentration is maintained at all times. The velocity constant is given by Now K will vary with the electrolyte concentration, and the resulting change in the concentration of the collision complex will cause a change in the measured velocity constant R. These changes have been observed for the hydrolysis of the acetals and for the inversion of sucrose, but even in dilute solution they seem larger than one would expect, by analogy, from an examination of the change, with electrolyte concentration, of the dis-(1) E. I. du Pont de Nemoun and Company Fellow, 1938. (2) Riesch and Kilpatrick, J . Phys. Chcm., 89, 561 (1935). (3) For references and discussion see Bonhoeffer, Trans. Faraday (4) Pedersen, ibid., 84, 237 (1938). (5) Hammett and Paul, THIS JOURNAL, 56, 830 (1934). (6) Gross, Steiner and Suess, Trans. Faraday Soc., 83, 883 (1936). (7) These experiments were camed out in this Laboratory in 1929 Sac., 84, 262 (1938). by M. L. Kilpatrick. sociation constant of anilinium or o-chloroaniliniumPedersen determined these two equilibrium constants over a convenient range of temperature, and found no great change in the heat of dissociation (MI') with temperature, in contrast to the marked variation of the heat of dissociation with temperature for uncharged acids. By analogy it might be expected that for reactions between a non-electrolyte and an ion, as represented by equation (1) , there would be little change with temperature in EA, the heat of activation computed from the integrated form of the Arrhenius equation (3)where k T , and kT, are the velocity constants at temperatures TI and Tz, respectively. This seems to be the case for the hydrolysis of diethyl acetals2An examination of the extensive literature on sucrose inversion (on which some excellent experimental work has been done) yields a n q b e r of surprises. For example, in a recent number of THIS JOURNAL we have "The activation energy of 25.7 f 0.05 kcal. found in the present work on sucrose is i...
Communications to the Editor Vol. 60 hydrochloride show that there is but one break in the titration curve when all the chloride ion has been neutralized, the formula for the vitamin is CgHnNOg-HCl.The absorption spectrum studies of the vitamin hydrochloride in acid, alkaline and neutral solutions indicate that we are dealing with a compound with tautomeric properties.Vitamin B-6 shows pronounced and welldefined absorption in the spectral region from 2300 to 3300 Á. In dilute hydrochloric acid (pO. 2) there is a single band with maximum absorption at 2925 Á. The hydrochloride dissolved in water (pa 4.5) shows that the band at 2925 Á. diminished in intensity along with a new band with maximum absorption at 3275 Á.At pa 6.75 the band at 3275 Á. has increased markedly while that at 2925 Á. has disappeared and simultaneously a new band at 2560 Á. has appeared. At pa 10.2 the two bands which were present at pa 6.75 have increased in intensity and shifted toward the shorter wave lengths.
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